Electrical systems can include devices for switching electric power. For example, an electromechanical relay can include one or more contacts for switching power from a power source to a load device. An armature of a relay can be moved between a first position that prevents current flow between the power source and the load and a second position that allows current flow between the power source and the load. For instance, in the first position, the relay may provide an open circuit between the power source and the load and, in the second position, the relay may provide a closed circuit between the power source and the load.
In these electrical systems, one or more devices may be used to detect the duration of the movement of an armature of a relay. Detecting the actuation duration of the relay can allow the operational lifespan of the relay to be increased. For example, the actuation duration can be used for switching power to a load at a point at which a sinusoidal input voltage or current from a power source has a zero value (“a zero-crossing”). Setting a relay to a closed position at or near a point in time associated with the zero-crossing of the input line voltage can significantly reduce or completely eliminate an inrush current to a capacitive reactive load.
Prior solutions for monitoring relays involve utilizing a voltage detector to detect a zero-voltage cross and a relay actuation (i.e., contact closure) delay time. These prior solutions may be used to identify a contact closure that is referenced to a zero-crossing of a current or voltage waveform.
These prior solutions may present disadvantages. One disadvantage is that using a voltage detector to detect a zero-cross may not account for current that could be leading or lagging the voltage, which may cause an adverse effect on the expected lifetime of the relay. For example, the waveform (and zero-crossing point) of an AC input voltage waveform may differ from the waveform (and zero-crossing point) of a current through a load. This difference may lead to inaccuracies in determining a zero-crossing point for the load current.
Another disadvantage of prior solutions is that using a separate voltage detector requires additional components that decrease overall reliability and increase the overall cost of an electrical device. For example, an electrical device may use a voltage-specific (e.g., 120 Vac or 277 Vac) detection method or device to detect a line voltage's zero-cross point and to synchronize a relay switching algorithm with the zero-cross point of the line voltage. The electrical device may use a separate current sense device to measure the load current through the load. The electrical device may also use separate contact sense circuitry to measure relay actuation delay time. Using these different sets of sensing circuitry can significantly increase the complexity of the electrical device's design and decrease the overall reliability of the electrical device.
Accordingly, improved systems and methods are desirable for determining the actuation duration of a relay and performing other functions that involve monitoring relay current.